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Discussion Starter · #1 ·
Hey-
I think there is a calc somewhere for this, but not can't find it. I have a Raleigh MCM carbon frame with vert drops that I would like to convert to SS to give it a whirl and see if it is my style. I don't want to run a tensioner or anything, just pure SS. I like the frame alot, can't afford another right now, and would much rather just convert this to SS. So, without taking it all apart and gettin dirty, is there a way to see if there is a gear that I can run without a tensioner? This would be a trail bike, so based on what I've read around here a 2:1 is what I am looking for. I already have a 36 tooth non-ramped chain ring that I would like to use if possible, and the back whatever will fit without a tensioner.

Unless of course someone wants to trade the MCM (same as the Giant frame) for a sweet steel SS frame. I am running a 17 or 18" frame I think, don't think this one was a 16" 'er.

Thanks,
Jason
 

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I like this program best.....

http://www.peak.org/~fixin/personal/fmu/php/fmu1_1_big.php

If you know your chainstay length, should be a snap to see if you can run sans tensioner. Based on this calculator (and info frm others on this board), I was able to figure out that the 16.75" stays on my Kona take a 32:18 or 34:20 very nicely without a tensioner. I ride the 34:20, and have never had problems.

Good luck to you,

-Que?
 

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Discussion Starter · #4 ·
Alright,
I ran them both. I am assuming center to center of the rear hub to the cranks is the measurement they are looking for. I am exactly 16 11/16", which is 16.69". With this the first one gives me (with the chain tension selection a little tight)
32x14 - Gain ratio = 4.31
34x16 - Gain ratio = 4.01
36x18 - Gain ratio = 3.77
The gain ratio I am assuming (based on the defintion) that it is the power transfer from your pedalling to the wheel.

The other calculater gave me:
Just a little under 16.69"
32x14
34x16
36x18 - chain length 47" and chain stay 16.688"

There are some more choices in the second calc, but are farther from my length, but are still in the shaded blue area, which I am assuming is cool.

So, based on your experience, is the 36x18 gears (2:1) ratio cool for fire roads and single track with alot of climbing? I know I will end up experimenting, but I would like to start out at a good ratio so as not to be disappointed by SS'ing.

Thanks,
Jason
 

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Most people around here recommend 2:1 gear ratio. For my '02 Fisher Hoo Koo E Koo I was able to run 32:18 (1.78:1) without a tensioner, so that is what I did. I have not been SS'ing for that long but heading up 2+ mile uphill trails is pretty tough even with that ratio.

IMHO, I would try the 36:18, from some old geary parts for one ride. If you like it, then go spring the $$ on the non-ramped/pinned ring and cog. I think you might have trouble keeping the chain on the 32:14, the 14 is pretty small.

Anyone else run a 14 with no tensioner?

What ever ratio you pick, be sure to get the non-ramped/pinned ring and cog version.
 

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Discussion Starter · #6 ·
Yea, I will see if I can pick up an 18tooth cog non-ramped somewhere local, maybe even pick up a 32 tooth non-ramped chain ring. The extra 32 tooth ring I have is four bolt and the cranks on the Raleigh are old school Cooks Cranks or Cooks Racing Cranks, which are 5 bolt. My current 36 tooth chain ring for the cranks is non-ramped.

Anybody know any local shops in Marin County that might have the rear cog? I am in Larkspur.

I think 32 / 18 will work without a tensioner. I'll try the 36 / 18 first to see if I can get up any hills. I think I may try to ride a Mt. Tam trail tomorrow on my geary- first ride there, second ride here in CA.

Jason
 

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calculators and avoiding the singleator

i don't know if you guys are still watching this thread but in caes anyone is here goes . . . just set up my fisher mt tam with non ramped 32 t up front (spot) and leftover-from-cogset (ie, ramped) 18 t in the back, with teh singleator b/c i had already bought it, made the chain tight as possible and it seems to fit great, may push the cog closer to the frame a bit to get the chainline straighter right now there's a spacer b/t cog and end of the spacing kit . . . anyway, i'm not real good at breaking and then reattaching my chain (my chain tool is to be replaced very shortly, as well as my chain) but i'm wondering if i'm using these calculators correctly which seem to tell me that i should be able to run 32:18 (my chainstays measure at 16.25, running 175 mm cranks) . . . as to the calculators, perhaps because i'm not mathematically minded, but if i ended up in the shaded blue on the fixed innovations page; i ran the calculations from team bigtime, and that's a great program esp as i am a mac user but i didn't understand how knowing "gain" would tell me the answer i need: can i put my singleator on e-bay? you guys seem to know what you're doing so any ideas are appreciated . . . diulio, this was a great thread you started, thanks, even if i need to keep my tensioner
 

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I found that measuring the chain stay length accurately enough to make the calculators useful was very difficult. So I put on the chainring, cog, chain and then measured the dip in the chain - holding a yardstick across the top of the rings and pressing down on the center of the chain. With that data and the chain length the "exact" chain stay can be computed. RSN I will try to do this in javascript, in the meantime if your gearing doesn't work send me your data and I'll tell you the true chainstay length.
 

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I sat down with Autocad, Excel and my old trig knowledge to come up with an Excel spreadsheet that accurately estimates the chain length for a given chainstay length and cog and ring. I've been running single/fixed on "magic gears" for about 4 years now. You'll have to replace your chain a little more often, but it can be cheaper than an Eno hub.

One tip: once you find a gear that works (and that you like), buy a singlespeed-specific cog (like a Chris King stainless cog). The ramped cogs from cassettes don't have sufficient tooth height, and you'll bounce the chain off on occassion - always at the least opportune time.
 

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Francis said:
I sat down with Autocad, Excel and my old trig knowledge to come up with an Excel spreadsheet that accurately estimates the chain length for a given chainstay length and cog and ring. I've been running single/fixed on "magic gears" for about 4 years now. You'll have to replace your chain a little more often, but it can be cheaper than an Eno hub.
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That's what the other online calculators do, when the chain length is a whole number they say voila. However minor errors in chainstay length can give gear ratios that are too tight or too loose. The measurement must be from axle center to BB center and in the same plane as the chain line. If you have a gear ratio that has a loose chain you can measure the dip of the chain and from that get the real chainstay length and go on your merry way with the other calculators. Essentially, you don't have to measure the chainstay at all.
 
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